The development, known as “Lotus Riverside,” has a total of 629 units, 489 of which have already been sold. Now buyers are clamoring to get their money back, and authorities are making efforts to reassure them. The assets of the project’s developer, Shanghai Meidu Property Development Co., have been frozen and the city officials said the developer’s ability to repay homebuyers was secure, according to a statement on the municipal government’s Web site (in Chinese). A hotline has been set up for Lotus Riverside buyers, and by Sunday afternoon, more than half of them had met with a group of lawyers and officials organized to help them negotiate with the developer, according to the statement.

Meanwhile, the cause of the accident is under investigation and nine unidentified people from the developer, contractor and management company have been detained.

A representative of Shanghai Meidu could not be reached for comment.

The disaster could reveal some uncomfortable facts about lax construction practices in China, where buildings are put up in a hurry by largely unskilled migrant workers, and developers may be tempted to take shortcuts.

According to Shanghai Daily, initial investigations attribute the accident to the excavations for the construction of a garage under the collapsed building. Large quantities of earth were removed and dumped in a landfill next to a nearby creek; the weight of the earth caused the river bank to collapse, which, in turn, allowed water to seep into the ground, creating a muddy foundation for the building that toppled.